Film and image heating device using film

ABSTRACT

A cylindrical film used in an image heating device heating a recording material, on which an image has been formed, has a resin layer, this resin layer being made from a resin in which a crystalline resin and an amorphous resin having a higher glass transition temperature than the crystalline resin are blended, wherein a volume ratio of the crystalline resin with respect to the amorphous resin in the resin layer is 70/30 to 99/1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/196,765, filed Jun. 29, 2016, which is adivisional application of U.S. patent application Ser. No. 14/847,406,filed Sep. 8, 2015, now U.S. Pat. No. 9,411,282, which is a divisionalapplication of U.S. patent application Ser. No. 14/467,294, filed Aug.25, 2014, now U.S. Pat. No. 9,158,251, which claims the benefit ofJapanese Patent Application No. 2013-178924, filed Aug. 30, 2013,Japanese Patent Application No. 2013-178925, filed Aug. 30, 2013, andJapanese Patent Application No. 2013-178926, filed Aug. 30, 2013. All ofthese prior applications are hereby incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a film which is used in an imageheating device, such as a fixing apparatus.

Description of the Related Art

An image-forming apparatus, such as an electrophotographic copyingmachine, electrophotographic printer, or the like, is provided with animage-forming unit which forms a toner image on a recording medium, anda fixing apparatus (image heating device) which carries out a heatingprocess so as to fix the toner image onto the recording medium, forinstance. The fixing apparatus forms a nip portion between a fixingrotating member and a pressing rotating member which rotate inpressurized contact with each other, whereby a recording medium on whichan unfixed toner image has been formed by the image-forming unit isheated while being gripped and conveyed, thereby fixing the toner imageonto the recording medium.

In a fixing apparatus of this kind, conventionally, a heat-resistantthin-film fixing film, for example, is used as a fixing rotating memberor a pressurizing rotating member. Japanese Patent ApplicationPublication No. 3-25481 discloses using a thermoplastic resin, such aspolyether ether ketone (PEEK), polyether sulfone (PESU), polyether imide(PEI), or the like, as material for the fixing film. A thermoplasticresin can employ a method of manufacturing such as extrusion molding,and therefore has an advantage in that it can be produced inexpensivelycompared to a thermosetting resin.

However, if a thermoplastic resin is used as the material for a fixingfilm, then there is a concern that fatigue cracks may occur due to theinsufficient bending resistance. On the other hand, if a thermoplasticfilm is used as the material of the fixing film, then there is apossibility of increase in the abrasion of the inner circumferentialsurface of the film due to insufficient abrasion resistance, and thereare concerns about the occurrence of slipping of the fixing film due tothe resistance caused by the abrasive dust.

SUMMARY OF THE INVENTION

One preferred embodiment of the invention of the present application isa cylindrical film used in an image heating device heating a recordingmedium on which an image has been formed, the cylindrical filmcomprising:

a resin layer, this resin layer being made from a resin in which acrystalline resin and an amorphous resin having a higher glasstransition temperature than the crystalline resin are blended,

wherein a volume ratio of the crystalline resin with respect to theamorphous resin in the resin layer is 70/30 to 99/1.

Second preferred embodiment of the invention of the present applicationis an image heating device performing a heating process for heatingwhile conveying a recording material on which an image has been formedin a nip portion, comprising:

a cylindrical film, this film having a resin layer made from a resin inwhich a crystalline resin and an amorphous resin having a higher glasstransition temperature than the crystalline resin are blended;

a nip portion forming member that contacts an inner surface of the film;and

a back-up member that forms the nip portion together with the nipportion forming member, via the film,

wherein a volume ratio of the crystalline resin with respect to theamorphous resin in the resin layer is 70/30 to 99/1.

Third preferred embodiment of the invention of the present applicationis a cylindrical film used in an image heating device heating arecording material on which an image has been formed, comprising:

a resin layer in which crystalline polyaryl ketone and an amorphousresin having a higher glass transition temperature than the crystallinepolyaryl ketone are blended,

wherein the resin layer has two or more glass transition temperaturesmeasured by differential scanning calorimetric measurement.

Fourth preferred embodiment of the invention of the present applicationis a cylindrical film used in an image heating device heating arecording material on which an image has been formed, comprising:

a resin layer made from crystalline thermoplastic resin, the degree ofcrystallinity of the resin layer being not less than 81% of the maximumsaturated degree of crystallinity of the crystalline thermoplasticresin.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general cross-sectional diagram of an image-forming devicerelating to an embodiment of the present invention;

FIGS. 2A to 2C are diagrams showing a configuration of a fixingapparatus relating to an embodiment of the present invention;

FIG. 3 is a general cross-sectional diagram of an image-forming devicerelating to a first embodiment of the present invention;

FIG. 4 is a diagram representing temporal change in the temperature ofthe film relating to the first embodiment of the present invention;

FIG. 5 is a conceptual diagram representing the liability to abrasion ofcrystalline resin and amorphous resin;

FIG. 6 is a diagram representing the volume ratio of PEEK and thebending resistance;

FIGS. 7A to 7C are schematic drawings representing a dispersed state ofa base layer of a film;

FIG. 8 is a diagram representing the volume ratio of PEEK and the amountof abrasion;

FIG. 9 is a schematic drawings representing an estimation mechanism forsuppressing abrasion of the film relating to the first embodiment;

FIG. 10 is a schematic cross-sectional diagram showing a furtherconfiguration of a fixing apparatus relating to an embodiment of thepresent invention;

FIG. 11 is a schematic cross-sectional diagram showing a furtherconfiguration of a fixing apparatus relating to an embodiment of thepresent invention;

FIG. 12 shows the results of a MIT test for a fixing film relating to asixth embodiment;

FIG. 13 shows the results of DSC for a fixing film relating to the sixthembodiment;

FIG. 14 is a schematic diagram of a fixing apparatus relating to thesixth embodiment;

FIG. 15 shows the relationship between the annealing time and the degreeof crystallinity;

FIG. 16 shows the lengthwise temperature distribution of a fixing beltduring the passage of paper;

FIG. 17 shows the external diameter distribution of a fixing belt afterthe passage of paper in the sixth embodiment and a sixth comparativeexample;

FIG. 18 shows the external diameter ratio of a fixing belt and the rateof occurrence of paper wrinkling;

FIG. 19 shows the external diameter ratio of the fixing belt and thedegree of crystallinity;

FIG. 20 shows the temperature of the fixing belt and the elasticity ofthe fixing belt; and

FIG. 21 is a cross-sectional diagram of a fixing apparatus relating to aseventh embodiment.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

(1) Image-Forming Apparatus

FIG. 1 is a schematic cross-sectional diagram showing the schematiccomposition of an image-forming apparatus (full-color printer) 100relating to the embodiment of the present invention. Here, theimage-forming apparatus forms an image on a recording medium, bydeveloper (toner), using an electrophotographic image forming process.For example, the image-forming apparatus includes an electrophotographiccopying machine, an electrophotographic printer (LED printer, laser beamprinter, etc.), an electrophotographic facsimile apparatus, anelectrophotographic word processor, or a machine combining these(multi-function printer), and the like. Furthermore, the recordingmedium is an article on which an image is formed, and is, for example,recording paper, an OHP sheet, a plastic sheet, cloth, or the like.

The image-forming unit which forms a toner image on the recording mediumP is composed by four image-forming stations Pa, Pb, Pc, Pd. Theimage-forming stations each have a photosensitive body 117, a chargingmember 119, a lens scanner 118, a developer 120, a transfer member 124,and a cleaner 122 for cleaning the photosensitive body. Moreover, theimage-forming unit has a belt (intermediate transfer member) 123 whichholds and conveys the toner image, and a secondary transfer roller 121which transfers a toner image from the belt 123 onto the recordingmedium P. The operation of the abovementioned image-forming unit iswell-known, and therefore detailed explanation thereof is omitted here.

The recording medium P is paid out, one sheet at a time, from thecassette 102, by the rotation of the roller 105, and this recordingmember P is conveyed to a secondary transfer nip portion which is formedby the belt 123 and the secondary transfer roller 121, due to therotation of the roller 106. The belt 123 is spanned tensely between atensioning roller 125 a and a secondary transfer opposing roller 125 b,and is rotated by the rotation of these rollers. The secondary transferopposing roller 125 b is made to contact the secondary transfer roller121 via the belt 123, whereby the abovementioned secondary transfer nipportion is formed. The recording medium P to which an unfixed tonerimage has been transferred in the secondary transfer nip portion isconveyed to the fixing unit 109, whereby the toner image is heated andfixed. The recording medium P exiting the fixing unit 109 is dischargedonto a tray 112 by the rotation of the roller 111.

(2) Fixing Unit (Fixing Apparatus) 109

The fixing apparatus which constitutes the fixing unit 109 will now bedescribed with reference to FIGS. 2A to 2C. FIG. 2A is a cross-sectionaldiagram showing the schematic composition configuration of the fixingapparatus 109 relating to the present embodiment. FIG. 2B is a frontview diagram showing the fixing apparatus 109 relating to the presentembodiment from the upstream side in terms of the direction ofconveyance of the recording medium. FIG. 2C is a diagram showing theschematic configuration of a ceramic heater 15 of the fixing apparatus109 relating to the present embodiment.

The fixing apparatus 109 has a heating unit 10 and a pressurizing roller30 forming a pressurizing member. The heating unit 10 includes a tubularfilm (endless film) 16, a film guide 19 forming a supporting member, anda ceramic heater (heat source) 15, or the like, forming a nip portionforming member. The film 16, the film guide 19, the ceramic heater(called “heater” below) 15 and the pressurizing roller 30 are eachmembers which are long in the direction perpendicular to the directionof conveyance of the recording medium (see FIG. 2A).

The heater 15 which forms a heat generating member is supported on thefilm guide 19, and the tubular film 16 having flexibility is fittedloosely onto the outside of the film guide 19. By gripping the film 16between the heater 15 and the pressurizing roller 30, a nip portion N isformed by the film 16 and the pressurizing roller 30.

Below, the respective members are described in more detail. Thepressurizing roller 30 has a round axle-shaped core metal core (axlesection) 30A made from a metal material such as iron, stainless steel,aluminum, or the like. An elastic layer 30B having silicone rubber, orthe like, as a main component, is formed in a roller shape on the outercircumferential surface between the support shaft sections 30A1 oneither end portion of the metal core 30A in the lengthwise direction(see FIG. 2B). Moreover, a separating layer 30C having PTFE, PFA or FEP,or the like, as a main component is formed on the outer circumferentialsurface of the elastic layer 30B. The support shaft sections 30A1 oneither end of the metal core 30A in the lengthwise direction aresupported rotatably via bearings 41 on left and right side plates 40which constitute a portion of the metal frame 39 of the fixing apparatus109.

The film guide 19 is formed with a substantially concave lateralcross-section, using a prescribed heat-resistant material. A groove 19Ais formed along the lengthwise direction in the flat surface of filmguide 19 on the side of the pressurizing roller 30. This groove supportsthe heater 15.

The heater 15 has a thin plate-shaped heater base plate 15A of which themain component is a ceramic, such as alumina, aluminum nitride, or thelike. An electric heat generating resistance 15B of which the maincomponent is silver, palladium, or the like, is printed as a patternalong the lengthwise direction of the heater base plate, on a filmsliding surface of the heater base plate 15A on the side of the film 16.Furthermore, a conducting section 15C for passing current to theelectric heat generating resistance 15B and an electrode section 15D forsupplying current to the electric heat generating resistance via theconducting section are printed as a pattern on the film sliding surface.Furthermore, a protective layer 15E of which the main component is glassor fluorine resin, or a heat-resistant resin, such as polyimide, isprovided on the film sliding surface so as to cover the electric heatgenerating resistance 15B.

The film 16 is formed in a cylindrical shape in such a manner that theinner circumferential length of the film is longer than the outercircumferential length of the film guide 19, and is loosely fittedexternally onto the film guide in a tension-free state. The layerconfiguration and the material of the film 16 is described below.

The film 16 fitted externally onto the film guide 19 is arranged inparallel with the pressurizing roller 30, and the film guide 19 isimpelled in a horizontal direction in which the respective ends in thelengthwise direction intersect perpendicularly with the bus direction ofthe pressurizing roller via pressurizing springs 42. The heater 15supported by the film guide 19 causes the film 16 to make contact withthe outer circumferential surface (front surface) of the pressurizingroller in a pressurized state, due to the pressing force of thepressurizing springs 42. Thereby, the elastic layer 30B of thepressurizing roller 30 is sunken and elastically deformed, and a nipportion N of a prescribed width (see FIG. 2A) is formed between thesurface of the pressurizing roller 30 and the outer circumferentialsurface (front surface) of the film 16.

In FIG. 2A, reference numeral 43 is a guide which guides a recordingmedium P to a nip portion N. Reference numeral 44 is a guide whichguides a recording medium P output from a nip portion N.

Referring to FIGS. 2A and 2C, a heating and fixing process operation ofthe fixing apparatus 109 will be described. The drive force of a motor(not illustrated) provided in the image-forming apparatus is transmittedto a gear (not illustrated) provided in the end portion of thelengthwise direction of the metal core 30A of the pressurizing roller30, whereby the pressurizing roller 30 is caused to rotate in thedirection of the arrow. The film 16 rotates in the direction of thearrow in accordance with the rotation of the pressurizing roller 30,while the inner circumferential surface (inner surface) of the film 16slides against the protective layer 15E of the heater 15.

Current is passed through the heat generating resistance 15B of theheater 15 via a triac 202, by a commercial power source 203, whereby theconductive heating resistance generates heat and the heater warms up.The triac 202 is controlled by a control unit 200 consisting of a CPUand a memory such as a RAM, ROM, or the like, in such a manner that thedetection temperature of the temperature detection element 201 thatmonitors the temperature of the non-sliding film surface of the heaterbase plate 15A is maintained at a fixed temperature (targettemperature).

The recording medium P which bears an unfixed toner image T is guided tothe nip portion N by the guide 43. While the recording medium P isgripped and conveyed by the nip portion N, the heat of the heater 15 andthe pressure of the nip portion are applied to the unfixed toner imageT, whereby the unfixed toner image T is heated and fixed onto therecording medium P. The recording medium P exiting the nip portion N isguided by the guide 44 and sent to the roller 111.

(3) Film 16

The film 16 is a round cylindrical shape having an outer diameter of 18mm, and has a mold separating layer 16B made of 30 μm-thick PFA providedon top of a 120 μm-thick base layer 16A (FIG. 3). Desirably, the averagevalue of the overall thickness of the base layer 16A is in a range of 50to 400 μm, and more desirably, in a range of 70 to 200 μm. If the fixingfilm is too thin, then it tends to become difficult to achieve a uniformthickness. On the other hand, if the fixing film is too thick, then theflexibility tends to decline. The film 16 is turned at a speed of 170mm/sec at the outer circumferential surface, while being pressed by theheater 15 at a pressure of 15 kg by the pressurizing roller 30.

The main component of the base layer 16A is a thermoplastic resin. Athermoplastic resin does not require a thermosetting step, as in thecase of a thermosetting resin, and therefore when manufacturing the film16, it is possible to employ a commonly known simple method, such asextrusion molding, injection molding, blow forming, inflation filmmolding, and the like. In the present embodiment, extrusion molding isused as the method of manufacturing the film 16.

Thermoplastic films can be divided broadly on the basis of thecrystalline properties into two types: crystalline resin, such as PEEK,and amorphous resin, such as sulfonated polyether imide (sulfonatedPEI), polyphenyl sulfone (PPSU), or the like. In the present embodiment,the material used for the base layer 16A is a blended resin whichcombines 70% by volume ratio of crystalline resin, and 30% by volumeratio of amorphous resin. PEEK (381G made by Victrex, Tg=143° C.) wasused as a crystalline resin, and sulfonated PEI (Ultem XH6050 made bySABIC, Tg=247° C.) was used as an amorphous resin.

If there are concerns about charging up during image formation, and ifimprovement in the mechanical strength is required, then a filler may beadded to the base layer 16A. Examples of the added filler are, forinstance, carbon black, graphite powder, carbon nanotubes, metal powder,metal oxide whiskers, and the like. Of these, carbon black is especiallydesirable from the viewpoint of mechanical properties. Examples ofcarbon black may include: ketjen black, acetylene black, oil furnaceblack, thermal black, and channel black. It is possible to use just oneof these types of carbon black, or to combine two or more of these typesof carbon black. The particle size of the filler is not less than 3 nmand less than 1000 nm, and more desirably, not less than 5 nm and lessthan 300 nm. If the particle size of the filler is too small, then thehandling during addition to the resin may become more difficult. If theparticle size of the filler is too large, then it may be difficult toforma film shape. Furthermore, the ratio of the filler in the resincomposition of the film is not less than 1 part by mass and no more than40 parts by mass with respect to 100 parts by mass of the thermoplasticresin, and more desirably, not less than 3 parts by mass and no morethan 20 parts by mass. If the ratio of filler is too large, then themechanical properties may decline due to increase in the brittleness ofthe fixing film. If the ratio of filler is too small, then the volumeresistivity of the fixing film may become too high. Moreover, the film16 used was a film from which residual stress occurring during moldingwas removed by an annealing process, and furthermore a crystallizationprocess was carried out in order to obtain the required initial strengthand thermal resistance.

Next, the temperature state of the film 16 during a heating and fixingprocess operation of the fixing apparatus 109 will be described.Although it depends on the thickness and size of the recording medium Pused, the fixing film 16 is heated to a range of approximately 80° C. toapproximately 240° C. during image formation.

FIG. 4 shows the evolution of the temperature of the film 16 when usingA4-size paper having a basis weight of 80 g/cm² (Red Label 80 made byCanon), as the recording medium P. The temperature of the film 16 israised to 165° C. by the heater 15, by the time that the recordingmedium P arrives at the nip portion N. When the recording medium P ispassing through the nip portion N, the temperature of the film 16becomes 165° C.

(4) Fatigue Cracks and Slipping of the Fixing Film

A conventional film 16 uses only crystalline resin, or only amorphousresin, as the material of the base layer. If only crystalline resin isused as the material of the base layer of the film 16, then abrasion(wear) is liable to occur, and if only amorphous resin is used as thematerial of the base layer of the film 16, then fatigue cracks areliable to occur.

Firstly, fatigue cracks in a conventional film 16 will be described inconcrete terms. The curvature of the film 16 varies with the position inthe circumferential direction, due to receiving forces from thepressurizing roller 30 in the nip portion N. Therefore, the film 16 isbent repeatedly when the film 16 is rotated. For instance, if only anamorphous resin is used as the material for the film 16, then cracks(so-called fatigue cracks) may occur due to this repeated bending. Thereason for this is that amorphous resin is generally weak againstrepeated bending stresses.

Next, abrasion of a conventional film 16 will be described in concreteterms. The film slides against the heater 15 at a temperature of 165° C.(processing temperature). For example, if the material of the film 16 isa single thermoplastic resin, then when the film 16 exceeds the glasstransition temperature Tg of the thermoplastic resin, then the abrasionof the film becomes dramatically worse (FIG. 5). This is because themovement of the molecules in the amorphous portion is activated when thetemperature goes above the glass transition temperature Tg, and theresin suddenly becomes soft. If there is large abrasion of the film inthis way, then the frictional resistance between the film 16 and theheater 15 becomes larger due to the viscosity of the abrasive powder,and slipping may occur which prevents the film 16 from rotating inaccordance with the roller. If slipping occurs, non-uniformities arisein the transmission of the heat to the recording medium P, andnon-uniformities arise in the luster of the image. Crystalline resin hasstronger resistance to fatigue cracks than amorphous resin, but usuallyhas a lower glass transition temperature Tg than amorphous resin. Inother words, with a conventional film 16, it is difficult to addressboth abrasion and fatigue cracks at the same time.

(5) Suppression of Fatigue Cracks and Slipping in Film 16

Firstly, a fatigue crack suppressing effect of the present embodimentwill be described. The relationship between the blending ratio of a 120μm-thick film formed by extrusion molding of a blended resin of PEEK andsulfonated PEI and the bending strength thereof at 165° C. is shown inFIG. 6. The bending strength was measured in compliance with JIS-P8115(2001), except for the fact that testing was carried out while heatingthe film to 165° C. with a hot air current. From the measurementresults, it can be seen that the bending strength varies greatly whenthe volume ratio of the PEEK is in a range of 30% to 70%, and does notchange significantly outside of this range. In other words, when thevolume ratio of PEEK is not less than 70%, then the bending strength canbe increased to substantially the same level as when the volume ratio ofPEEK is 100%.

Furthermore, when a 120 μm-thick film formed by extrusion molding of ablended resin of PEEK and sulfonated PEI was observed with a TEM, itcould be seen that the dispersed state of the PEEK phase 60 a and thesulfonated PEI phase 60 b changes with the volume ratio of the PEEK, asshown in FIGS. 7A to 7C. FIG. 7A is a schematic diagram of a phasecomposition when the volume ratio of the PEEK is less than or equal to30%, FIG. 7B is a schematic diagram of a phase composition where thevolume ratio of PEEK is greater than 30% and less than 70%, and FIG. 7Cis a schematic diagram of a phase composition when the PEEK volume ratiois equal to or greater than 70%.

Here, the reason why the bending strength can be improved by setting thevolume ratio of the PEEK to be not less than 70%, and adopting the phasecomposition shown in FIG. 7C, was inferred by the present inventors tobe that indicated below. Sulfonated PEI, which is an amorphous resin, isweak against repeated bending stresses, and therefore the sulfonated PEIphase 60 b is liable to form starting points of cracks. If thesulfonated PEI phase 60 b is disposed or isolated in island shapes, theneven if cracks occur in the sulfonated PEI, the advance of the cracks isrestricted by the PEEK phase 60 a, and therefore this does not leaddirectly to fatigue cracks. On the other hand, if the sulfonated PEIphase 60 b is joined in a continuous fashion, then a crack will advanceprogressively in the sulfonated PEI phase 60 b only, without passing viaa PEEK phase 60 a, and therefore the fatigue cracks become worse.

Next, the abrasion suppressing effects of a film 16 relating to thepresent embodiment will be described. The relationship between theblending ratio of a 120 μm-thick film formed by extrusion molding of ablended resin of PEEK and sulfonated PEI and the amount of abrasionthereof at 165° C. is shown in FIG. 8. The amount of abrasion is takento be the amount of weight change in the film 16 when the roller 105 wasrotated for 120 hours while heating the heater 15 so as to achieve atemperature of 165° C. of the film 16, in a composition where the blendratio of the film 16 of the fixing unit 109 of the present embodimentwas varied. From the measurement results, it can be seen that the amountof abrasion varies greatly when the volume ratio of the PEEK is in arange of 100% to 90%, and does not change significantly outside of thisrange. In particular, the amount of abrasion changes greatly when thevolume ratio of the PEEK is in a range of 100% to 99%. In other words,even if a small amount of sulfonated PEI is blended with the PEEK, theabrasion resistance can be improved. The reason for this was inferred bythe present inventors to be that described below.

The blending materials of the polymer blend according to the presentembodiment were selected to be PEEK which has a glass transitiontemperature Tg (143° C.) which is lower than the temperature of 165° C.used in the heat treatment of the film 16, and sulfonated PEI which hasa glass transition temperature Tg (247° C.) that is higher than saidtemperature. Therefore, at the use temperature 165° C. of the film 16,the PEEK phase 60 a is soft and the sulfonated PEI phase 60 b is hard.Therefore, the PEEK phase 60 a of the film 16 wears preferentiallyduring use, and as shown in FIG. 9, the sulfonated PEI phase 60 bassumes a surface state of projecting beyond the surface of the PEEKphase 60 a. Therefore, the hard sulfonated PEI phase 60 b receives themajority of the force from the heater 15. Thereafter, the soft PEEKphase 60 a is not liable to receive force from the heater 15, andtherefore the abrasion of the PEEK phase 60 a becomes less liable toadvance.

From the foregoing, in the present embodiment, the blending volume ratio(A/B) of the crystalline resin (A) and the amorphous resin (B) in theblended resin used in the base layer 16A of the film 16 is between 70/30and 99/1. The effects of the present embodiment in suppressing fatiguecracks and suppressing slipping were confirmed in actual practice. Morespecifically, the fatigue cracks after passing 50,000 sheets and theslipping after passing 50,000 sheets in the composition of the presentembodiment were evaluated. The paper sheets passed where Red Label 80.As a first comparative example, compositions were prepared in which thevolume ratio (%) of the thermoplastic resins in the material of the baselayer 16A of the first embodiment was changed to PEEK/sulfonatedPEI=100/0, 50/50, 0/100. Table 1 shows the evaluation results. As shownin Table 1, it can be seen that the first embodiment is able to suppressboth fatigue cracks and slipping.

TABLE 1 Volume ratio (%) Sulfonated PEEK PEI Fatigue cracks SlippingEmbodiment 1 70 30 ◯ ◯ Comparative 100 0 ◯ X Example 1 50 50 X ◯ 0 100 X◯

Second Embodiment

The film relating to a second embodiment of the present invention is nowdescribed. Here, principally, only the points which are different to thefirst embodiment are explained, and the composition which is similar tothe first embodiment is labelled with the same reference numerals and isnot described further here. Matters which are not described here aresimilar to the first embodiment.

In the present embodiment, the same composition as the first embodimentwas adopted entirely, apart from the fact that polyether ketone etherketone ketone (PEKEKK) was used as a crystalline resin, and PPSU wasused as an amorphous resin. More specifically, in the presentembodiment, the material used for the base layer 16A is a blended resinwhich combines 70% by volume ratio of crystalline resin, and 30% byvolume ratio of amorphous resin. PEKEKK (HT made by Victrex, Tg=162° C.)was used for the crystalline resin, and PPSU (Radel R R-5000 made bySolvay Advanced Polymers (today's Solvay Specialty Polymers), Tg=220°C.) was used for the amorphous resin.

The effects of the present embodiment in suppressing fatigue cracks andsuppressing slipping were confirmed in actual practice. The method ofevaluation was the same as that employed in the first embodiment. As asecond comparative example, compositions were prepared in which thevolume ratio (%) of the thermoplastic resins in the material of the baselayer 16A was changed to PEKEKK/PPSU=100/0, 50/50, 0/100. Table 2 showsthe evaluation results.

TABLE 2 Volume ratio (%) PEKEKK PPSU Fatigue cracks Slipping Embodiment2 70 30 ◯ ◯ Comparative 100 0 ◯ X Example 2 50 50 X ◯ 0 100 X ◯

It can be seen that in the second embodiment, it is possible to suppressboth fatigue cracks and slipping. In other words, even with a blendedresin containing PEKEKK and PPSU, by making the volume ratio of thecrystalline resin not less than 70%, it is possible to suppress bothfatigue cracks and slipping.

As described in the present embodiment, the combination of thecrystalline resin and the amorphous resin in the material of the baselayer 16A is not limited to PEKEKK and PPSU, provided that a combinationis adopted in which the Tg of the amorphous resin is higher than thecrystalline resin.

Furthermore, since the base layer 16A may deteriorate when tonercomponents, and the like, become attached thereto, then a crystallinepolyaryl ether ketone resin having excellent chemical resistance issuitable as the crystalline resin. The crystalline polyaryl ether ketoneresin is a crystalline resin including a homopolymer, copolymer,terpolymer, grafted copolymer, or the like, which contains a monomerunit including one or more aryl groups, one or more ether groups and oneor more ketone groups. For example, this resin can be selected fromamong: PEEK, PEKEKK, polyether ketone (PEK), polyether ketone ketone(PEKK), polyaryl ether ketone ether ketone ketone (PAEKEKK), polyarylether ketone (PAEK), polyaryl ether ether ketone (PAEEK), polyetherether ketone ketone (PEEKK), polyaryl ether ketone ketone (PAEKK),polyaryl ether ether ketone ketone (PAEEKK), and the like. If themelting point is low, then the resin melting temperature whenmanufacturing the base layer 16 a can be lowered, and it is especiallydesirable to use PEEK as the crystalline resin, since this facilitatesmanufacture. Furthermore, when using a crystalline polyaryl ether ketoneresin, the amorphous resin is desirably a resin having a glasstransition temperature Tg which is sufficiently higher than the glasstransition temperature Tg of the crystalline polyaryl ether ketoneresin. Examples of resins of this kind are, for instance, sulfonatedPEI, PPSU, PESU, polysulfone (PSU), and the like. Of these, sulfonatedPEI has a particularly high glass transition temperature Tg, andtherefore if used as the material of the base layer 16A, has a merit inpermitting reduction of the restrictions on the through-put of recordingmedia P having a narrow width. The reason for this is described below.

When recording medium P of narrow width is passed, the temperature ofthe portion of the film 16 in the lengthwise direction where paper isnot passed becomes higher than the temperature of the portion wherepassed is passed. In this case, the through-put of the recording mediumP must be slowed, in order that the temperature of the portion of thefilm 16 where paper is not passed does not exceed the glass transitiontemperature Tg of the amorphous resin. This is because if thetemperature of the portion of the film 16 where the paper is not passedexceeds the glass transition temperature Tg of the amorphous resin, thenthe rigidity of the film 16 declines suddenly and this may lead tobreakdown of the film. Therefore, by using sulfonated PEI which has ahigh glass transition temperature Tg for the amorphous resin, it ispossible to reduce restrictions on the through-put of the recordingmedium P.

Furthermore, it is also possible to use a plurality of crystallineresins and to use a plurality of amorphous resins as the material of thebase layer 16A. Moreover, for instance, it is also possible to use acombination of any one of, or a plurality of, PEEK, PEK and PEKEKK, as acrystalline resin, and any one of, or a plurality of, sulfonated PEI,PPSU and PESU, as an amorphous resin.

Furthermore, the film 16 according to the first embodiment and thesecond embodiment was used in a composition having a heat source on theinner side of the film 16, but the present embodiment is not limited tothis composition. Any composition may be adopted, provided that the film16 undergoes repeated bending at or above the Tg temperature of thecrystalline resin, and that the film 16 slides over the nip portionforming member 15 at or above the Tg temperature of the crystallineresin. For instance, as shown in FIG. 10, it is possible to adopt acomposition in which a heat source 61 (halogen heater) is incorporatedinside the metal core 60A. Furthermore, for example, it is also possibleto adopt a composition including a heat source 62 which heats the outercircumferential surface of the pressurizing roller 30, as shown in FIG.11. Moreover, a fixing apparatus having a halogen heater incorporatedinside the film 16 may be used.

In each of the embodiments described above, an example is given in whichthe invention is applied to a heat fixing apparatus which fixes an imageto a recording medium by applying heat, but the range of application ofthe present invention is not limited to this. For example, the presentinvention may be applied widely to apparatuses for providing a heattreatment on a medium receiving application of heat, such as an imageheating device for modifying the surface of a recording medium, so as tocreate a luster on the surface of the recording medium by heating, animage heating device for provisional fixing, a heating and dryingapparatus for a medium receiving application of heat, a heating laminateapparatus, and the like.

In the present embodiment, there are no particular restrictions on themethod for confirming the volume ratio of the blended resin. Forexample, it is possible to use a commonly known method in which anultra-thin cut piece is created by cutting the base layer 16A in aprescribed direction, is dyed with ruthenium tetroxide (RuO4), or thelike, and is observed with an transmission electron microscope (TEM), orthe like. In the case of this method, for example, the surface arearatio of each resin phase in the material of the base layer 16A, in across-section of the base layer 16A, is the volume ratio.

Third Embodiment

The image-forming apparatus and the fixing apparatus according to thepresent embodiment is the same as the first embodiment, with theexception of the film 16, and therefore description thereof is omittedhere. Furthermore, since the basic composition of the film 16 is thesame as the first embodiment, description thereof is omitted here. Thepoint of difference with the film of the first embodiment is describedin detail here. As stated in the first embodiment, the fixing film 16 isheated to a range of approximately 80° C. to approximately 240° C.during the fixing process. Furthermore, as described above, the fixingfilm 16 makes contact in a state of being pressurized by the outercircumferential surface of the pressurizing roller 30, and thereforerotates in a twisted and deformed state within the range of elasticdeformation. For the reasons given above, it is important that thefixing film 16 should maintain thermal resistance in a broad range, andbending resistance within the range of elastic deformation, during theproduct lifespan.

The object of the present embodiment is to provide a fixing film havinghigher bending resistance, which is a round cylindrical fixing filmcreated by extrusion molding using a blended resin of PEEK and PEI thatdemonstrate good compatibility.

(4) Differences Between Comparative Examples and Embodiments

In the method for manufacturing a fixing film, the fixing filmsaccording to embodiment 3-1, embodiment 3-2 and comparative examples 3to 5 were manufactured by the same method, except for the fact that thecomposition of the blended resin used in the base layer 16A was changedto the compositions indicated in Table 3.

Table 3 shows the results of confirming the performance of comparativeexamples 3 to 5 and embodiments 3-1 and 3-2.

TABLE 3 Performance evaluation Added filler Bending Resin parts by mass(100) w.r.t. 100 Tensile Bending resistance Sulfonated parts byelasticity Thermal resistance (afterdurability PEEK PEI PEI mass ofresin GPa 160° C. resistance (new) testing) Comparative 100 0 0 0 0.76NG OK OK example 3 Comparative 0 0 100 0 1.41 OK NG NG example 4Comparative 70 30 0 0 1.08 OK OK NG example 5 Embodiment 70 0 30 0 1.04OK OK OK 3-1 Embodiment 70 0 30 0 1.20 OK OK OK 3-2

Comparative example 3 is a fixing film made from PEEK only. This fixingfilm has a low thermal resistance, and has a possibility of breaking ordeforming during image formation. This is because the glass transitiontemperature (Tg) of the PEEK (Victrex 381G) is 143° C., which is lowerthan the use temperature range. The glass transition temperature of thesulfonated PEI (Sabic Ultem XH 6050) shown in comparative example 4 is ahigh value of 247° C., but since this resin is an amorphous resin andhas poor bending resistance, then there is a possibility of fracturingof the fixing film, and so on.

Comparative example 5 is a blended resin of PEEK (Victrex 381G) and PEI(Ultem #1000) which have good compatibility. The fixing film made fromblended resin disclosed in comparative example 5 does not present anyproblems in terms of thermal resistance and bending resistance when new,but upon confirming the durability using an image-forming apparatus, adecline in the bending resistance after durability testing was observed.

On the other hand, in embodiment 3-1, there was no deterioration in thethermal resistance or the bending resistance throughout the lifespan ofthe image-forming apparatus, and no problematic defect was observed. Inembodiment 3-2, ten parts of a conductive filler was added to 100 partsby mass of the blended resin in embodiment 3-1, and by setting anappropriate amount of filler, the bending resistance did not present anyproblems, both initially and after durability testing, and goodperformance could be obtained.

The difference between comparative example 3 and embodiments 3-1 and 3-2can be regarded as due to the fatigue of the film bending resistance.This is now described by using the results of MIT testing according toJIS P 8115 (bending resistance test method).

With regard to the test conditions, the radius of curvature of thebending surface of a bending clamp was 0.38 mm, the width of the testpiece was 10±0.1, the load was 9.8 N, and the bending angle was 135±2°.The number of bending operations until the test piece broke was taken tobe the bending resistance number.

FIG. 12 shows the MIT test results when new, and the MIT test resultsafter durability testing using an image-forming apparatus, forcomparative example 5, embodiment 3-1 and embodiment 3-2. In the case ofthe combination of materials in comparative example 3, the MIT numberdeclined markedly after durability testing. On the other hand, it can beseen that the fixing film having the materials in embodiments 3-1 and3-2 showed little decline in the MIT before and after durabilitytesting, and hence the bending resistance was stable throughout theproduct life.

The difference in durability between comparative example 5 andembodiments 3-1 and 3-2 is considered by the present inventors to be dueto the state of mixing of the blended resin. The inferred mechanism forthis is described below.

When forming a fixing film with a material made from a blended resin, itis considered that the state of mixing between the resins forming theblended resin is important. If the resins are not mixed with each other,then it is attempted to form a thin film, the film forming propertiesdecline and it is difficult to form the film shape, and there may becases where the film shape can be formed, and the film does not have themechanical strength required for practical use. On the other hand, inthe case of a blended resin which is completely mixed as in comparativeexample 5, these resins are mixed together at the molecular level, and afilm can be formed without any problem.

However, when a completely mixed blended resin is used as a fixing filmin an image-forming apparatus, it surmised that the bending resistancedeteriorates during the growth process of crystallization. If the PEEKis exposed to high temperatures, the crystallization is promoted, butthe progress of crystallization of the PEEK inside the blended resinwhich is completely mixed at the molecular level is considered to becrystallization progressing in a state where the PEI which has goodcompatibility is wrapped inside the crystal nuclei of the PEEK. In otherwords, it is considered that the bending resistance declines in thecomparative example, because of the growth of crystal nuclei in whichthe PEI, which has inferior bending resistance to the PEEK, isincorporated inside the crystal nuclei of the PEEK. On the other hand,in the present embodiment, the PEEK and the sulfonated PEI form a smoothmixed state. Since the grain interfaces which form the unmixed portionare present in sufficiently small units compared to the thickness of thefilm, then the film formation properties are good and a film havingsufficient mechanical strength is obtained. The present inventorsconsidered that there is no decline in the bending resistance when ablended resin having a gradual mixed state of this kind is used as afixing film in an image-forming apparatus, due to the fact that thecrystallization of the PEEK occurs without the sulfonated PEI becomingincorporated inside the crystal nuclei of the PEEK.

(5) Results of Differential Scanning Calorimetric Measurement (DSC) inComparative Example 5 and Embodiment 3

Differential scanning calorimetric measurement (DSC) is used here toexplain the differences between comparative example 5 and embodiment 3,as indicated below. Firstly, the method of measuring the glasstransition temperature (Tg) in the present embodiment will be described.

5 to 20 mg, and desirably, 10 mg, of a measurement sample was weighedout precisely. This sample was introduced into an aluminum pan, andusing the empty aluminum pan as a reference, was measured in a measuredtemperature range of 80° C. to 380° C., at a ramp rate of 10° C./min.The apparatus used for measurement was a Mettler Toledo DSC 823.

A: PEEK 100 parts by mass

B: PEEK 70 parts by mass/PEI 30 parts by mass (comparative example 5)

C: PEEK 70 parts by mass/sulfonated PEI 30 parts by mass (embodiment3-1)

As shown in FIG. 13B, in comparative example 5, one glass transitiontemperature was observed (B_(PEEK)), at 159° C., despite the fact thatthe resin was a blended resin of two types: PEEK (Tg 143° C.) and PEI(Tg 217° C.). In other words, the glass transition temperature of thePEEK in comparative example 5 showed a higher result than the glasstransition temperature for 100 parts by mass of PEEK (pure PEEK)(A_(PEEK)=143° C.)

It is generally known that the glass transition temperature in a casewhere resins having different glass transition temperatures, Tg1 andTg2, are blended and completely mixed together is given by the FOXequation which is shown in Expression (1). In comparative example 5, theobserved glass transition temperature (159° C.) is substantiallyconsistent with the glass transition temperature (159.4° C.) obtainedfrom the FOX equation, and therefore the blended resin in comparativeexample 5 is considered to have the PEEK and the PEI in a completelymixed state.

$\begin{matrix}{\frac{1}{T_{g}} = {\frac{w_{1}}{T_{g,1}} + {\frac{w_{2}}{T_{g,2}}.}}} & \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack\end{matrix}$

-   (W₁ and W₂ are the respective weight ratios of the resins) Formula    (1)

On the other hand, in the case of embodiment 3-1 shown in FIG. 13C,there are two observed glass transition temperatures, which are causedby the PEEK (C_(PEEK)) and the sulfonated PEI (C_(S) ⁻ _(PEI)). Theglass transition temperature due to the PEEK (C_(PEEK)) observed inembodiment 3-1 is 145° C., and the glass transition temperature(A_(PEEK)) of the 100 parts by mass of the PEEK (pure PEEK) is virtuallythe same. On the other hand, it was confirmed that the glass transitiontemperature (C_(S) ⁻ _(PEI)) due to the sulfonated PEI is in thevicinity of 230° C., which is shifted to the lower temperature side fromthe glass transition temperature of pure sulfonated PEI, which is 247°C. The present inventors considered that this is because the sulfonatedPEI and the PEEK form a gradual mixed state, rather than a completelyunmixed state.

It is considered that, by setting two or more glass transitiontemperatures for the blended resin as described above, a gradual mixedstate is formed. Therefore, the blended resin used in the presentembodiment has two or more glass transition temperatures measured in thedifferential scanning calorimetric measurement. Furthermore, desirably,the glass transition temperature due to the amorphous resin which ismeasured by the differential scanning calorimetric measurement of theblended resin is lower than the glass transition temperature of theamorphous resin measured by the differential scanning calorimetricmeasurement.

Furthermore, from the results of the tensile elasticity measurement in afilm state, it can be seen that the materials of the present embodimentform a gradual mixed state, rather than a completely unmixed state.Table 1 shows the results of measuring the tensile elasticity using a100 μm-thick film in a 160° C. environment.

In the present invention, the tensile elasticity of the 100 μm-thickfilm in the 160° C. environment was measured by a method compliant withJIS 7127.

In comparative example 1, which is pure PEEK, decline in the elasticityis observed when the glass transition temperature is exceeded, and thetensile elasticity in a 160° C. environment was 0.76 GPa. The sulfonatedPEI in comparative example 4 was at or below the glass transitiontemperature in the 160° C. environment, and had a high elasticity of1.41 GPa. Comparative example 5, which is a blended resin having highcompatibility, had an elasticity of 1.08 GPa, the elasticity beingraised due to the addition of PEI. This is thought to be because areinforcing effect due to the addition of PEI is obtained in the filmstate, due to the high compatibility between the resins in comparativeexample 3 and the excellent film forming properties. On the other hand,in embodiment 3-1, the tensile elasticity was 1.04 GPa, and theelasticity was improved by the addition of sulfonated PEI. Furthermore,in the embodiment 3-2, a further improvement in the elasticity wasobserved due to the addition of a filler. For this reason also, theembodiments 3-1 and 3-2 have excellent film forming properties and areconsidered to show a gradual mixed state. This same tendency wasobserved in a film thickness range of 50 to 150 μm. As described above,in the present invention, under the environment at the temperature of160° C., the tensile elasticity of a 100 μm-thick film-shaped sample isdesirably higher in the case of a blended resin, than in the case of acrystalline polyaryl ketone resin.

The present inventors made the following observations with regard to themechanism by which the blended resin of sulfonated PEI and PEEK shown inembodiment 3-1 forms a smooth mixed state without being completelymixed.

As shown by Structural Formula (1) below, the structure of sulfonatedPEI includes a sulfonyl group having a large polarity in the main chainof the PEI. The PEEK and PEI essentially have very high compatibility,but due to the presence of sulfonyl groups containing sulfur which arehighly polarized, the electrostatic forces due to polarization affectthe interactions between molecules, and the compatibility with PEEKpartially becomes incompatible. In this way, desirably, the amorphousresin used in the blended resin relating to the present invention is aresin having a group of large polarity, such as a sulfonyl group, in themain chain.

The amorphous resin used in the present embodiment is a resin which isformed from any one, or at least two of: sulfonated polyether imide(PEI), polyether sulfone (PES), polyphenyl sulfone (PPSU), andpolysulfone (PSf).

As described above, by achieving a gradual mixed state between thecrystalline polyaryl ketone resin and the amorphous resin, good filmforming properties are guaranteed, and it is possible to provide afixing film in which there is no deterioration of bending resistance dueto the advance of crystallization as a result of use underhigh-temperature conditions.

Fourth Embodiment

The method for manufacturing a fixing film according to the presentembodiment differs from the third embodiment only in respect of thematerial of the fixing film used, and is the same as the thirdembodiment in all other respects, and therefore only the differences aredescribed here.

(6) Differences Between Comparative Examples and Embodiments

In the present embodiment also, the fixing film 16 forms a two-layerstructure. In embodiment 4-1 (see Table 4), the base layer 16A is ablended resin (90 μm thick) of PEEK (Victrex 381G, Tg 143° C.) which isa crystalline polyaryl ketone resin, and PPSU (Solvay Specialty PolymersRadel R R-5000, Tg 220° C.) which is an amorphous resin, and the surfacelayer 16B is made of PFA tube (DuPont 450 HP) (30 μm thick).

In embodiment 4-2, the base layer 16A is a blended resin (90 thick) ofPEEK (Victrex 381G, Tg 143° C.) which is a crystalline polyaryl ketoneresin, and PES (Solvay Specialty Polymers Radel Polyether sulfone, Tg220° C.) which is an amorphous resin, and the surface layer 16B is madeof PFA tube (DuPont 450 HP) (30 μm thick).

In both of embodiments 4-1 and 4-2, the average value of the overallthickness of the fixing film 16 was 120 μm.

The results of a performance comparison carried out with the fixing film16 of the present embodiment and the film 16 of comparative example 5,using the image-forming apparatus described above, are shown in Table 4.Embodiment 4-1 showed little deterioration in either the thermalresistance or the bending resistance throughout the lifespan of theimage-forming apparatus. In embodiment 4-1, similarly, although PPSU wasused as the amorphous resin, there was little deterioration duringdurability testing. Furthermore, the tensile elasticity in a 100μm-thick film state was also similar to that of comparative example 5 inwhich the resins are completely mixed (see Table 4).

Furthermore, the Tg of the blended resin in the fixing film inembodiment 4-1 was 150° C. and 210° C. (due to the amorphous resin), andthe Tg of the blended resin in the fixing film in embodiment 4-2 was152° C. and 208° C. (due to the amorphous resin).

TABLE 4 Performance evaluation Bending Tensile Bending resistance Resinparts by mass (100) elasticity Thermal resistance (afterdurability PEEKPEI PES PPSU GPa 160° C. resistance (new) testing) Comparative 70 30 0 01.08 OK OK NG Example 5 Embodiment 70 0 30 0 1.04 OK OK OK 4-1Embodiment 70 0 0 30 1.00 OK OK OK 4-2

Due to the matters described above, although the resins are notcompletely mixed in both embodiments 4-1 and 4-2, since the resins aredispersed in very small units, then it is possible to obtain sufficientmechanical strength. Furthermore, it is thought that, by making the PEEKnot mix completely with the amorphous resin, then upon crystallizationof the PEEK, the crystal nuclei of the PEEK grow separately from theamorphous resin, and therefore the deterioration due to durabilitytesting is slight.

The structural formulae for PPSU and PES are indicated below. In bothcases, the structure includes a sulfonyl group in a main chain. Asstated previously, the sulfonyl group includes sulfur and has largepolarity. It is inferred that, due to the effects of the electrostaticforces caused by polarization of the sulfonyl group, on the molecularinteractions with the PEEK, the compatibility with the PEEK partiallybecomes incompatible.

As described above, by setting the blended resin of crystalline polyarylketone resin and PPSU, and the blended resin of crystalline polyarylketone resin and PES to a gradual mixed state, the good film formationproperties are guaranteed, and it is possible to provide a fixing filmshowing little deterioration in the bending resistance due to theadvance of crystallization when used at high temperatures.

Fifth Embodiment

In the present embodiment, the fixing apparatus used is different.Below, the composition is described with reference to FIG. 14. A fixingroller 410 inside which a heat source 420, such as a halogen lamp, isprovided, together with a fixing film 16 which grips and conveys paperby rolling with the fixing roller 410, and a fixing pad 460 which isarranged in contact with the inner circumferential side of a tubularfixing film 16 and which forms a fixing nip N between the fixing roller410 and the fixing film 16. The fixing pad 460 in the present embodimentis composed by a pressing pad 460 a which is a low-pressure pad sectiondisposed on the upstream side, and a fixed pad 460 b which is ahigh-pressure pad disposed on the downstream side having a higherpressing force than the pressing pad 460 a, these pads being arranged ina separated state, in such a manner that the fixing nip width is similarfrom the central portion of the fixing pad 460 to both ends thereof. Thepressing pad 460 a and the fixed pad 460 b are supported by a rigidsupporting body 470 having a depressed portion for supporting the pads(460 a and 460 b), and press the fixing film 16 against the surface ofthe fixing roller 410 from the rear surface side of the fixing film 16.Moreover, a belt travel guide 45 made from a rigid resin having lowthermal conductivity, for example, is provided below the rigidsupporting body 470 in order that the fixing film 16 rotates smoothly.

Furthermore, a temperature sensor 490 which measures the surfacetemperature of the fixing roller 410 is disposed in the periphery of thefixing roller 410, and the temperature of the heat source 420 iscontrolled by the temperature sensor 49 in such a manner that thesurface temperature of the fixing roller 410 becomes a prescribedtemperature. There are no particular restrictions on the temperaturesensor 490, provided that the sensor is capable of measuring the surfacetemperature of the fixing roller 410, and it is possible to use a sensorelement such as a thermistor, Posistor, or the like, for example.

The fixing roller 410 according to the present embodiment is constitutedby a round cylindrical core 410 a made from a metal such as aluminum,which has excellent mechanical strength and good thermal conductivity,an elastic layer 410 b such as silicone rubber, which is formed on thesurface of the core 410 a, and a separating layer 410 c which is laid onthe surface of the elastic layer 410 b and is provided in order toprevent offsetting of the unfixed toner image on the paper.

Here, there are no particular restrictions on the material of the core410 a, provided that the material has mechanical strength and goodthermal conductivity, and there is no problem in using a metal or alloysuch as stainless steel, steel or brass. Furthermore, the elastic layer410 b is not limited to silicone rubber, and provided that the layer hasthermal resistance, it is possible to use fluorine rubber, for example.The method for forming the elastic layer 410 b on the surface of thecore 410 a is not limited in particular either, and an injection formingmethod, a coating method, or the like, may be adopted. Moreover, theseparating layer 410 c is required to have thermal resistance and beprovided with adequate separating properties with respect to toner, andmay use fluorine rubber, fluorine resin, or the like, for instance.Furthermore, there are no particular restrictions on the heat source 420inside the fixing roller 410, provided that the heat source has a shapeand a structure that enable accommodation thereof inside the core 410 a,and the heat source can be selected appropriately in accordance with theobject, without any problem.

(7) Description of Fixing Film 16 Relating to the Present Embodiment

The fixing film according to the fifth embodiment was manufacturedsimilarly to embodiment 3-1, using a blended resin (120 μm thick) ofPEEK (Victrex 381G, Tg 143° C.) which is a crystalline polyaryl ketoneresin and a PSf (Solvay Advanced Polymers UDEL P-1700, Tg 189° C.) whichis an amorphous resin, and as a surface layer 16B, PFA tube (DuPont450HP) (30 μm thick). In the fifth embodiment, the blend ratio in thebase layer 16A was 70 parts by mass of PEEK and 30 parts by mass of PSf,with respect to 100 parts by mass of resin. The average value of theoverall thickness of the fixing film 16 was 100 μm. The Tg value of theblended resin in the fixing film according to the fifth embodiment was148° C. and 180° C. (due to the amorphous resin). Furthermore, thetensile elasticity (100 μm-thick film) in a 160° C. environment was GPa.

In the fixing apparatus according to the present embodiment, a fixingroller 41 having a three-layer structure, and a recording medium, arepresent between the fixing film 16 and the heat source 42. Therefore,the heat from the heat source 42 is not liable to cause the fixing film16 to reach a high temperature, due to the effects of the thermalresistance of the member.

Even in the embodiment described above, the blended resin can form agradual mixed state, there is no problem with thermal resistance andbending resistance, and it is possible to provide a fixing film whichshows little deterioration throughout the life of the image-formingapparatus.

Below, the structural formula for PSf is indicated. The PSf also has astructure that includes a sulfonyl group in a main chain. As statedpreviously, the sulfonyl group includes sulfur and has large polarity.It is inferred that, due to the effects of the electrostatic forcescaused by polarization of the sulfonyl group, on the molecularinteractions with the PEEK, the compatibility with the PEEK partiallybecomes incompatible.

As described above, by achieving a gradual mixed state in thecrystalline polyaryl ketone resin and the PSf blended resin, good filmforming properties are guaranteed, and it is possible to provide afixing film in which there is little exacerbation in bending resistancedue to the advance of crystallization as a result of use at hightemperatures.

Sixth Embodiment

The image-forming apparatus and the fixing apparatus relating to thepresent embodiment are the same as the first embodiment, and thereforedescription thereof is omitted here. A thermoplastic endless fixing belt(film) may have an increased degree of crystallinity and a contractedexternal diameter. After continuous passing of paper of small size, suchas A5 paper, there may be virtually no variation of the externaldiameter in the portion where the paper passes and there may besignificant contraction of the external diameter in the portion wherethe paper does not pass. It is known that, with this film, wrinkles areliable to occur in the paper when paper of large size is passed, such asletter size or A4 paper.

An object of the present embodiment is to provide a fixing belt whichcan suppress the occurrence of wrinkles in the paper, even if this beltis formed from thermoplastic resin.

The fixing belt according to the sixth embodiment has the followingmethod of manufacture and characteristic features. PEEK (Victrex 381G)was selected as the thermoplastic resin, and was extruded from anextrusion forming apparatus. The extruded resin passes through aring-shaped die, and upon cooling, is formed into a hollow-shaped belt.In this case, the belt has a lengthwise-direction length of 260 mm, anexternal diameter of 18.6 mm, and a film thickness of 100 μm, and is ina substantially non-crystallized state.

Next, a primer is applied uniformly to the outer circumferential surfaceof the belt, and is coated with PFA tube having a film thickness of 30μm (material: DuPont 950 HP). In this state, the belt is introduced intoa furnace at 220° C. (a DN610H air-blower thermostatic tank made byYamato Scientific Co., Ltd.), calcined for one hour, and the PFA tubeand the belt are bonded, simultaneously with which the degree ofcrystallinity of the PEEK is raised to substantially the maximumsaturated degree of crystallinity. Finally, both of the lengthwise endsof the hollow-shaped belt are cut, and the length in the lengthwisedirection is formed to 233 mm.

The maximum saturated degree of crystallinity referred to here means thedegree of crystallinity in a case where the PEEK material has beenheated sufficiently to the glass transition temperature of the PEEKmaterial or above, and when change in the degree of crystallinity haseffectively ceased to occur. FIG. 15 shows the degree of crystallinityof the PEEK material with respect to the time of introduction into thefurnace at 220° C. According to FIG. 15, it can be confirmed that thedegree of crystallinity is virtually saturated when annealing is carriedout for one hour or more. From FIG. 2, it can be determined that themaximum saturated degree of crystallinity in this case is 37%.

In this way, the fixing belt according to the present embodiment isformed by extrusion or injection, and desirably, the formed fixing beltis also subjected to an annealing process. In this annealing process,the fixing belt is calcined for 30 to 300 minutes at a temperature of143° C. to 250° C. at all times, thereby raising the degree ofcrystallinity.

The conditions for measuring the degree of crystallinity in the presentembodiment are as described below. Apparatus: Multipurpose X-raydiffraction system: Rigaku Ultima IV

Output: 40 kV-30 mA

Divergence slit: 2/3°

Vertical divergence slit limit: 10.00 mm

Scattering slit: 2/3°

Light-receiving slit: 0.30 mm

Measurement conditions: Concentrated beam method

Measurement rate: 5°/min

Measurement angle range: 2θ=5 to 45°

By the degree of crystallinity measurement described above, diffractionpeaks are obtained in both the amorphous portion and the crystallineportion of the PEEK material, and the degree of crystallinity (%) iscalculated by Expression (2) below, from the integrated intensity of thepeak at the diffraction angle of 2θ=5 to 45°.Degree of crystallinity(χc)=(integrated intensity of the crystallineportion/integrated intensity of the portion including amorphous andcrystalline material(2θ=5 to 45°))×100(%)  Expression (2)

The integrated intensity of the crystalline portion is the sum of therespective integrated intensities of the peaks which appear in thevicinity of 2θ=19° (110 face), the vicinity of 21° (113 face), thevicinity of 23° (200 face), and the vicinity of 29° (213 face).

By the process described above, a fixing belt having alengthwise-direction length of 233 mm, an external diameter of 18.2 mm,a film thickness of 130 μm, and made from a hollow PEEK material havinga degree of crystallinity of 37%, was formed. There are no particularrestrictions on the shape of the fixing belt according to the presentinvention, but desirably, the lengthwise-direction length is 216 to 320mm and the external diameter is 10 to 40 mm. Furthermore, desirably, thefilm thickness of the PEEK base material is approximately 50 to 200 μm.Moreover, in the case of a two-layer structure which is covered with PFAtube, as in the fixing belt of the present invention, the PFA tube isdesirably approximately 10 to 50 μm.

Furthermore, the fixing belt is installed in a fixing apparatus capableof thermally adhering the toner image to the paper.

Comparative example 6 is shown below.

Comparative Example 6

In a comparative example 6, a fixing belt is manufactured by using PEEKhaving a degree of crystallinity of 20% as the base material. The methodfor manufacturing the comparative example 6 is similar to embodiment 6,apart from the fact that the calcination time after extrusion was 5minutes.

In order to confirm the effects of the present embodiment, embodiment 6and comparative example 6 were compared as indicated below.

A total of 1000 postcards were passed through the fixing apparatus shownin FIG. 2, by repeating, 20 times, a 50-sheet continuous passage ofpostcard paper (100 mm wide by 148 mm high, 209.5 g/m²), at a rotationalspeed of 150 r/min. Thereupon, 100 sheets of Neenah Bond paper (215.9 mmwide by 279.4 mm high, 60 g/m²) were passed continuously, and theoccurrence of wrinkling in the paper was confirmed. Furthermore, thetarget temperature during the passage of paper was set to 150° C. andthe electric power input to the heater was controlled accordingly. FIG.16 shows the surface temperature distribution of the fixing belt duringthe passage of paper in this case. The surface temperature of the fixingbelt reached approximately 120° C. in the portion where the paperpassed, and approximately 200° C. in the portion where the paper did notpass.

Table 5 shows the results of a comparative study of the occurrence ofwrinkling in embodiment 6 and comparative example 6. In Table 5, when100 sheets of Neenah Bond paper were passed continuously, a case wherewrinkling occurred, even once, was marked as “X” and a case where nowrinkling occurred was marked as “◯”. In this case, embodiment 6 was “◯”and comparative example 6 was “X”. In embodiment 6, the effect ofsuppressing the occurrence of paper wrinkles due to the contraction ofthe external diameter of the fixing belt was confirmed.

The mechanism behind the suppression of paper wrinkles in embodiment 1is described below. FIG. 17 shows the external diameter distribution inthe lengthwise direction of the fixing belt after the comparative studybetween embodiment 6 and comparative example 6. According to this, inembodiment 6, the external diameter was a stable value of 18.2 mmthroughout the whole range in the lengthwise direction. On the otherhand, in comparative example 6, the external diameter is contractedgreatly in the locations other than the portion where the postcardpasses. This is because the crystallization of the PEEK in the fixingbelt is promoted in the portion where the paper does not pass, andtherefore the external diameter difference between the center and theends of the fixing belt is enlarged, giving rise to paper wrinkles.Next, attention was focused on the external diameter ratio between thecenter and the ends of the fixing belt, and a case where paper wrinklingoccurred was marked “X” and a case where wrinkling did not occur wasmarked “◯”. FIG. 18 shows the corresponding relationship between theexternal diameter ratio and the occurrence rate of paper wrinkling.

According to this, if the external diameter ratio exceeds 1.005 (theexternal diameter difference between the center and the ends of thefixing belt is 0.5%), then paper wrinkling occurs. The external diameterdifference occurs because there is a difference in the speed of movementbetween the portion of the fixing belt that makes contact with thecentral portion of the paper, and the portions thereof that make contactwith the ends of the paper. As a result of this, if distortion occurs inthe paper and this distortion exceeds a prescribed amount, then thisdistortion is manifested as paper wrinkles. In the present study, thinpaper (60 g/m²) which is liable to generate paper wrinkling even withlittle distortion was passed. Even with paper that differs from that ofthe present embodiment, provided that the ratio of the external diameterbetween the center and the ends of the fixing belt (center/end ratio) isless than 1.005 (and desirably, no more than 1.0045), it is consideredthat the occurrence of paper wrinkling can be suppressed.

FIG. 19 shows the relationship between the degree of crystallinity ofthe fixing belt after extrusion molding and the external diameter ratio(center/end) between the center and ends of the fixing belt in thelengthwise direction after the passage of paper. According to this, theexternal diameter ratio (center/end) of the fixing belt can besuppressed to less than 1.005, provided that the degree of crystallinityis not less than 30%. Furthermore, since the maximum saturated degree ofcrystallization of the PEEK used in embodiment 6 is 37%, then taking astate of saturated crystallization to be 100%, crystallization shouldproceed to not less than 81%. Consequently, the degree of crystallinityof the crystalline thermoplastic resin used in the fixing belt accordingto the present embodiment is not less than 81% (and desirably, not lessthan 86%) of the maximum saturated degree of crystallinity of thecrystalline thermoplastic resin. Furthermore, the degree ofcrystallinity of the crystalline thermoplastic resin used in the fixingbelt of the present embodiment is desirably not less than 30% (and moredesirably, not less than 32%).

From the results of embodiment 6 and comparative example 6 given above,it can be seen that the occurrence of paper wrinkling can be suppressedby installing, in a fixing apparatus, a fixing belt in which the degreeof crystallinity of the crystalline thermoplastic resin used in thefixing belt is not less than 81% with respect to the maximum saturateddegree of crystallinity of the crystalline thermoplastic resin material.

Next, in order to confirm the excellent high-temperature behavior in thepresent embodiment, an explanation is now given of the results of acomparative study into the difference in the bending resistance betweena case where a belt material using thermoplastic resin is installed in afixing apparatus as a fixing belt, and a case where the belt material isinstalled in a transfer apparatus as an intermediate transfer belt.Therefore, comparative example 7 was prepared and the bendingresistance, in other words, the presence or absence of cracking, wascompared. Comparative example 7 is described below.

In comparative example 7, a fixing belt was manufactured by using PEEKhaving a degree of crystallinity of 37% as the base material, similarlyto comparative example 6.

The paper passage conditions in comparative example 7 are indicatedbelow. To simulate installation in a transfer apparatus as anintermediate transfer belt, the target temperature was set to 50° C. andthe power input to the heater was controlled accordingly. The surfacetemperature of the fixing belt during the passage of paper in this casereached approximately 35° C. In other words, the conditions did notpermit a toner image to be adhered thermally to the paper.

On the other hand, in embodiment 6, it is presumed that the toner imagecan be adhered thermally to paper, and therefore the target temperatureof the fixing apparatus is set to 180° C. and the power input to theheater is controlled. The surface temperature of the fixing belt duringpassage of paper in this case reaches approximately 150° C., which is acondition that permits the toner image to be adhered thermally to thepaper.

In the comparative study, a total of 1000 sheets of paper were passedthrough the fixing apparatus shown in FIG. 1, by repeating, 20 times, a50-sheet continuous passage of Neenah Bond (215.9 mm wide by 279.4=high,60 g/m²), at a rotational speed of 150 r/min.

Table 5 shows the results of a comparative study of the occurrence ofcracking in embodiment 6 and comparative example 7. When a case wherecracks occurred in the fixing belt was marked as “X” and a case wherecracks did not occur was marked as “◯”, then embodiment 6 was marked “◯”and comparative example 7 was marked “X”. From the above, in embodiment6, it was confirmed that the bending resistance was satisfied andcracking could be suppressed, by installing a fixing belt made from aPEEK material in a fixing apparatus which thermally adheres a tonerimage to paper.

Here, the difference in bending resistance is considered in relation toembodiment 6 and comparative example 7. FIG. 7 shows the relationshipbetween the temperature of the fixing belt and the tensile elasticity ofthe fixing belt in this case. According to this, the tensile elasticityof the fixing belt declines greatly from the point where the temperatureof the fixing belt exceeds 143° C., which is the glass transitiontemperature (Tg) of the belt material. Furthermore, it is generallyknown that the tensile elasticity has a significant correlation with thebending resistance.

In embodiment 6, rotational operation is carried out in a temperaturerange in which the toner image can be melted, in other words, a statewhere the tensile elasticity of the fixing belt is low, and thereforethe bending resistance is excellent. On the other hand, in comparativeexample 7, the rotational operation is carried out in a temperaturerange in which the toner image cannot be melted, in other words, a statewhere the tensile elasticity of the fixing belt is high, and thisexacerbates bending resistance and therefore leads to cracking. In thisway, the fixing belt according to the present invention is desirablyused in a temperature range in which the toner image can be melted (80°C. to 140° C.), and especially desirably, is used at or above the glasstransition temperature of the crystalline thermoplastic resin of thefixing belt.

Table 5 shows a summary of the results of the comparative study ofembodiment 6, comparative example 6 and comparative example 7.

TABLE 5 Paper wrinkling Cracks Embodiment 6 ◯ ◯ Comparative X ◯ Example6 Comparative ◯ X Example 7

In a fixing belt used in a temperature range in which the toner imagecan be melted, it was confirmed that there is no need to be particularlyconcerned about deterioration of the bending resistance due to increasein the degree of crystallinity as has been envisaged in the prior art.Therefore, in embodiment 1, a fixing belt having a resin layer formedfrom a thermoplastic resin that can be manufactured inexpensively, isinstalled in a fixing apparatus, and the occurrence of paper wrinklescaused by contraction of the external diameter of the fixing belt can besuppressed, at the same time as satisfying the bending resistance.

In embodiment 6, although a fixing belt having a resin layer made fromPEEK which is a crystalline thermoplastic resin is used, in the presentembodiment, it is also possible to expect similar results when using aresin belonging to the same type of aromatic ether ketones. For example,it is possible to use a belt made from at least one or at least two orthe following crystalline thermoplastic resins: polyether ketone (PEK),polyether ether ketone (PEEK), polyether ketone ether ketone ketone(PEKEKK), polyether ketone ketone (PEKK), polyaryl ether ketone etherketone ketone (PAEKEKK), polyaryl ether ketone (PAEK), polyaryl etherether ketone (PAEEK), polyether ether ketone ketone (PEEKK), polyarylether ketone ketone (PAEKK), and polyaryl ether ether ketone ketone(PAEEKK). Of these, PEEK, PEK or PEKEKK is desirable.

Furthermore, even in a case where an additive or crystalline resin, orthe like, is blended with the crystalline thermoplastic resin, it ispossible to display a similar action and effects. Since the measurementvalue of the degree of crystallinity varies with the blend ratio, thenin the case of a blended material, by ascertaining the maximum saturateddegree of crystallinity in this blended material and specifying thedegree of crystallinity with respect to the maximum saturated degree ofcrystallinity, the action and effects indicated in embodiment 6 can bedisplayed, needless to say, and detailed description thereof is omittedhere. The fixing belt according to the present embodiment has a layerincluding a crystalline thermoplastic resin, but may also have atwo-layer structure. For instance, a layer including a crystallinethermoplastic resin may be used as a base material, and a resin, such asperfluoro alkoxy alkane (PFA), may be coated onto the outercircumferential surface of the layer including the crystallinethermoplastic resin. The coating resin may be one selected from a groupconsisting of perfluoro alkoxy alkane (PFA), polytetra fluoroethylene(PTFE), and the like.

Seventh Embodiment

(Description of Apparatus)

FIG. 8 shows a cross-sectional diagram of a fixing apparatus in theseventh embodiment, and an overview of the apparatus will be described.In the present embodiment, a surface heating fixing apparatus shown inFIG. 21 is used. In the present composition, the fixing belt 1 forms afixing nip N with the pressurizing roller 3, the surface of thepressurizing roller 3 is surface-heated by a separate heat roller, andthis heat is supplied to the recording material and the toner image T,thereby performing a fixing operation.

A heat roller 12 which incorporates a halogen heater 13 as a heatingsource is pressed against the pressurizing roller 3, thereby forming ahot pressure nip H. A fixing nip N is formed by the contact portionbetween the fixing belt 1 and the pressurizing roller 3, and when paperP bearing a toner image T is passed through this fixing nip N, the tonerimage on the paper P can be heated and fixed.

The belt guide 2 is formed by heat resistant resin, such as liquidcrystal polymer, PPS, PEEK, or the like, and the end portions in thelengthwise direction are coupled with fixing stays 7 which are supportedon the apparatus frame.

Pressurizing springs (not illustrated) apply pressure to the ends of thefixing stays 7 in the lengthwise direction, whereby the belt guide 2 ispressurized towards the side of the pressurizing roller 3. In this case,the pressurizing force applied to the pressurizing roller 3 is 160N andthe fixing nip N in this case is 6 mm. In order that the fixing stays 7transmits the pressurizing force received by both ends of the lengthwisedirection, in a uniform fashion in the lengthwise direction of the beltguide 2, a rigid material such as iron, stainless steel, pre-coated (onthe basis of Zinkote) steel plate, or the like, is used, and therigidity is increased by adopting a square U-shaped cross-sectionalshape.

Pressing sections (not illustrated) in both end portions of the heatroller 12 are pressed by pressurizing springs, and are pressurizedagainst the pressurizing roller 3. In this case, the pressurizing forceapplied to the pressurizing roller 3 is 160 N.

The temperature sensing element 6 contacts the surface of the heatroller 12, and the temperature of the fixing apparatus, in other wordsthe input power of the halogen heater 13, is controlled in accordancewith the sensing temperature of the temperature sensing element 6.

In this fixing apparatus, the pressurizing roller 3 and the heat roller12 rotate due to driving force from a motor (not illustrated) whichtransmits motive power to the pressurizing roller 3 and/or heat roller12, the paper P is conveyed by the frictional force acting between thesurface of the pressurizing roller 3, the fixing belt and the paper P,and the toner is heated and fixed.

The fixing apparatus used in this case differs from the fixing apparatusshown in FIG. 2 in that the heat roller, which is the heating source,and the fixing belt do not make direct contact with each other. In thepresent case, even with a fixing apparatus of this kind, the occurrenceof paper wrinkles is suppressed and the occurrence of cracks due to thebending resistance can also be suppressed.

Below, embodiment 7 is described. The fixing belt used was a fixing beltmanufactured similarly to embodiment 6, having a lengthwise-directionlength of 233 mm, an external diameter of 18.2 mm, a film thickness of130 μm, and made from a hollow PEEK material having a degree ofcrystallinity of 37% and PFA.

The composition of the pressurizing roller 3 in embodiment 7 is nowdescribed. A balloon rubber layer was formed to a thickness of 3.4 mm onan 11 mm-diameter steel core, a 150 μm-thick layer of rubber having highthermal conductivity was layered thereon, and further covered with 10μm-thick insulating PFA tube, the hardness being 56 degrees. The lengthof the elastic layer and the separating layer in the lengthwisedirection was 229 mm.

In embodiment 7, the presence or absence of paper wrinkles was confirmedunder the following conditions. A total of 1000 postcards were passed,by repeating, 20 times, a 50-sheet continuous passage of postcard paper(100 mm wide by 148 mm high, 209.5 g/m²), at a rotational speed of 150r/min. Thereupon, 100 sheets of Neenah Bond paper (215.9 mm wide by279.4 mm high, 60 g/m²) were passed continuously, and the occurrence ofwrinkling in the paper was confirmed. Furthermore, the targettemperature during the passage of paper was set to 220° C. and theelectric power input to the heater was controlled accordingly. Thesurface temperature of the fixing belt during this passage of the paperreached approximately 130° C. in the portion where the paper passed andreached approximately 200° C. in the portion where the paper did notpass.

Upon confirming the presence or absence of paper wrinkling in this case,it was found that paper wrinkling did not occur. Furthermore, theexternal diameter ratio (center/end) between the center and the ends ofthe fixing belt was 1.0005, and could thus be kept at or below a valueof 1.0045 at which a wrinkle suppressing effect is obtained.

Next, the presence or absence of cracking due to the passage of paperwas confirmed. As regards the paper passage conditions, the targettemperature during the passage of paper in the fixing apparatus was setto 220° C. and the electric power input to the heater was controlledaccordingly. Furthermore, after reaching the target temperature, controlwas implemented to start the passage of paper to the fixing apparatus.In this case, the temperature of the fixing belt reached 150° C.Furthermore, the paper which was passed at a rotational speed of 150r/min in the fixing apparatus was Neenah Bond paper (215.9 mm wide by279.4 mm high, 60 g/m²), and a 50-sheet paper passage operation wasrepeated 20 times, thereby passing a total of 1000 sheets, as a resultof which there was no occurrence at all of cracks in the fixing belt.

From the above, even in a system in which the heating source and thefixing belt make no contact, as in the fixing apparatus of embodiment 7,a fixing belt using a thermoplastic resin which can be manufacturedinexpensively is installed in a fixing apparatus, and the occurrence ofpaper wrinkles due to contraction of the external diameter of the fixingbelt can be suppressed, at the same time as satisfying the bendingresistance.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. A film unit used in a fixing apparatus having aheating roller, the film unit comprising: a cylindrical film including aresin layer, which is made from a crystalline thermoplastic resin,wherein a degree of crystallinity of the resin layer is not less than81% of a maximum saturated degree of crystallinity of the crystallinethermoplastic resin; and a nip forming member contacting an innersurface of the film, configured to form a nip portion with the heatingroller via the film, wherein an image is fixed on a recording materialby heat from the heating roller while the recording material, on whichthe image is formed, is being conveyed at the nip portion.
 2. The filmunit according to claim 1, wherein the degree of crystallinity of theresin layer is not less than 30%.
 3. The film unit according to claim 1,wherein the degree of crystallinity of the resin layer is not less than32%.
 4. The film unit according to claim 1, wherein the crystallinethermoplastic resin is a resin made from at least one of polyether etherketone, polyether ketone, and polyether ketone ether ketone ketone. 5.The film unit according to claim 1, wherein the degree of crystallinityof the resin layer is not less than 86% of the maximum saturated degreeof crystallinity of the crystalline thermoplastic resin.
 6. The filmunit according to claim 1, wherein the film is arranged in atension-free state.
 7. A fixing apparatus comprising: a cylindrical filmincluding a resin layer, which is made from a crystalline thermoplasticresin, wherein a degree of crystallinity of the resin layer is not lessthan 81% of a maximum saturated degree of crystallinity of thecrystalline thermoplastic resin; a pressure roller being in contact withan outer surface of the film; and a nip forming member contacting aninner surface of the film, configured to form a nip portion with thepressure roller via the film, wherein an image is fixed on a recordingmaterial by heat from the film while the recording material, on whichthe image is formed, is being conveyed at the nip portion.
 8. Theapparatus according to claim 7, wherein the nip forming member is aheater.
 9. A film unit used in a fixing apparatus, the film unitcomprising: a cylindrical film including a resin layer, which is madefrom a crystalline thermoplastic resin, wherein a degree ofcrystallinity of the resin layer is not less than 81% of a maximumsaturated degree of crystallinity of the crystalline thermoplasticresin; and a nip forming member contacting an inner surface of the film,configured to form a nip portion with a pressure roller mounted on thefixing apparatus via the film, wherein an image is fixed on a recordingmaterial by heat from the film while the recording material, on whichthe image is formed, is being conveyed at the nip portion.
 10. The unitaccording to claim 9, wherein the nip forming member is a heater.